Loudspeaker



March 24, 1936.

R. B. SCRIBNER 2,034,882

LOUDSPEAKER Filed May 24, 1953 2 Sheets-Sheet l INVENTOR. Eomqyn Saw/5n ATTORNEY Maj-ch 24, 1936. 1 R. B. SCRIBNER 2,034,882

LOUDSPEAKER Filed May 24, 1933 2 Sheets-Sheet 2 Patented Mar. 24, 1936 PATENT OFFICE LOUDSPEAKEE Romeyn B. Scribner, Rye, N. Y., assignor to Thomaston Laboratories, Inc., New York, N. Y., a corporation of New York Application May 24, 1933, Serial No. 672,580

My invention relates to amplifiers or loud speakers for radio telephone receivers and sound as well to high and low audio frequencies, so that the reproduction will be smooth and undistorted throughout the audible range.

A further object of the invention is to provide a diaphragm for a sound reproducing apparatus comprising two parts, one of which is particularly adapted to respond to high frequencies and the other to low frequencies, the two parts being so related as to blend the sound they produce.

A special object of the invention is to provide a loud speaker diaphragm driven by piezo-electric means.

There is a limit to the amount of voltage which may be impressed on a piezo-electric crystal beyond which the crystal will rupture. With a loud speaker of conventional design the movement necessary for satisfactory volume of sound calls for voltages which will bend the crystal to or beyond the rupture point. To overcome this difliculty I have devised a diaphragm which will cause suflicient damping so that a high voltage may be applied without causing the crystal to break and so that at the same time the diaphragm will impart to the air suificient movement to produce a satisfactory volume of sound. The mere increase in size of a diaphragm does not solve the problem because while the damping may thereby be increased to a point at which it will prevent rupture of the crystal, the weight and inertia of such a diaphragm causes a fall'- ing ofl in audible high frequency response, except at the edge of the diaphragm nearest to the driving unit. My invention takes advantage of the relatively faster and shorter movement adjacent the driving unit for producing the high frequency response and also embodies means for satisfactory reproduction of the lower frequencies. To this end I provide a composite diaphragm comprising a comparatively light and substantially rigid portion for high frequency response and mount this in connection with a larger and heavier portion for the low frequency oscillations. This design provides the necessary damping for the longer movements of low notes 3 Claims. (c1. 1s1-c2) portions will converge and blend so as to achieve an apparent non-directional effect.

Other objects and advantages will appear in the following description of several embodiments of my invention and thereafter the novelty and 5 scope of the invention will be pointed out in the claims.

In the accompanying drawings;

Figure 1 is a view in vertical section of a loud speaker embodying my invention, the section 10 being taken on the line l-I of Fig. 2;

Fig. 2 is a view in front elevation of the loud speaker shown in Fig. 1;

Fig. 3 is a fragmental view in vertical section of a loud speaker with the outer casing re- 15 moved showing the inner conical part of the diaphragm in the form of a truncated cone;

Fig. 4 is a view similar to that shown in Fig. 3 except that the inner part of the diaphragm is in the form of a hollow cone filled with 20 sound absorbent material;

Fig. 5 is a view in vertical section of a loud speaker with casing removed showing an inner cone integrally connected to the smaller end of an outer truncated cone;

Fig. 6 illustrates in vertical section another construction in which the inner portion of the diaphragm comprises a solid block having a convex sound projecting surface, and being driven by a single piezo-electric driver;

Fig. 7 is a view similar to Fig.'6 in which the central part of the diaphragm is in the form of a conical block and the diaphragm is driven by a plurality of piezo-electric devices;

Fig. 8 is a view similar to Fig. fi-showing hemi- 35 spherical block forming the central portion of the diaphragm with a plurality of crystal drivers connected to the center of said block;

Fig. 9 is a fragmental end view looking toward the right hand end of Fig. 8; 40

Fig. 10 is a view in perspective of a composite diaphragm of the type shown in Fig. l with a spider connecting the two diaphragm sections and a single driver for said spider;

Fig. 11 is a fragmental rear end view of a 45 composite diaphragm showing a spider driven by a plurality of piezo-electric devices; and

Fig. 12 is a fragmental view in vertical section of a composite diaphragm composed of an outer and inner portion flexibly connected to- 50 gether, each portion being separately driven by piezo-electric devices.

Referring to Figures 1 and 2, I show a casing IS in the form of a box, the front wall I 6 of which has a circular opening therein. In register with 55 said opening and projecting inwardly from the wall it is a diaphragm part il in the form of a frusto-conical wall. The conical part H is formed at its larger end with an outwardly directed flange I8 which is clamped between the wall it and a ring it. The diaphragm ii at its inner end is formed with an inwardly directed flange ifia. which is-clamped between a pair of rings 20 and 2 l A cone 22 with its apex directed outwardly forms the central part of the composite diaphragm and is provided at its base with an outwardly extending flange 23 which is also clamped between the rings 29 and 28.

Mounted on the rear wall 26 of the casing is a bracket 25 provided with four arms 26. Se-

. cured to each arm is a piezo-electric driver 2i,

the details of which are not shown as the driver may be of any well known commercial form. Each driveris connected by a link or driving rod 28 to the ring 29. It will be understood that all of the drivers are connected to a common source of, modulated electric energy and they act simultaneously to oscillate the ring 20 and thereby to oscillate not only the inner cone 23 but also the outer truncated cone ii of the diaphragm.

The inner cone is preferably formed of some stifi material such, for instance, as stifi paper, while the outer portion ll of the diaphragm is formed of a flexible material, such as cloth treated to render it non-porous without destroying its flexibility. The angle between the'outer facepi cone 22 and the inner face of the truncated cone is preferably about 90 degrees, although other angles may be used to effect the proper blending of sound from the two diaphragm parts. When thecone is vibrated by the drivers 2? the high frequencies will affect the stiff central cone portion while the larger flexible outer portion of the diaphragm will respond more readily to the lower frequencies. The sound waves thus produced will be blended provided the surfaces from which they originate form an angle of less than 186 degrees, because the waves which are gen-= erated by the inner cone section will be thrown across the path of the waves generated by the outer portion of the diaphragm. At a short distance from the loud speaker depending upon the angle between the sound generating surfaces it will be impossible to detect any directional eflect. This non-directional eifect is particularly useful in the illusion of talking or sound motion picture synchronization. The damping effect of this composite diaphragm will be sufficient to prevent the crystals from being bent beyond their rupture point and at the same time the diaphragm will respond to the higher frequencies because of the comparatively small, light and stifi central portion 22.

While I prefer to form the inner portion of the diaphragm as a complete cone this is not absolutely essential. For example, Fig. 3 shows a construction similar to that illustrated in Fig. l and the parts duplicated in the two illustrations bear the same reference numerals. The only dif-v ference between the two constructions is that.

the central portion of the composite diaphragm consists of a truncated cone 3% having an open- "ing 38 at its outer, smaller end. The truncated v the outer diaphragm part ii! between the rings 2t] and 2i.

The construction shown in Fig. 4 differs from stiff while the outer portion 35 is left flein'ble so that it will respond to the lower frequencies.

In Fig. 6 there is still another construction in which the central portion of the diaphragm consists of, a block Aid of some light solid material, such, for instance, as balsa wood. This block has a convex sound generating surface. The outer part ll of the diaphragm may be a duplicate of that shown in Fig. l and its flange i841. is clamped between the block db and a ring ii. A single piezo-electric driver '62 is connected by a driving rod d3 directly to the block dB.

Fig. 7 shows a'diaphragm somewhat similar to that shown in Fig. 6 except that a conical block $5 is substituted for the block db and a plurality of piezo-electric drivers ill are connected by driving rods M to a ring 19 which clamps the flange 08a to the cone 415.

In Figs. 8 and 9 there is a still difierent connection between the drivers and the diaphragm. In this case the central portion of diaphragm consists of hemispherical block 5t].

52 to a common driving rod 53 which in turn is connected. to the center of the block 5d. It will be observed that in the structures shown in Figs. 6 to 9 the central portion of the diaphragm vibrates as a whole because it consists of a solid block and this portion of the diaphragm responds to higher frequencies whereas the outer portion ii of the diaphragm will respond to the lower frequencies. While the inner portion of the diaphragm need not necessarily be conical; but is convex, as shown in Figs. 6 and 8, the effect is substantially the same as that produced with diaphragms having a conical center. The sound waves thrown oh by the outer portion of the di-; aphragm converge upon the sound waves generated by the inner portion i'l'and blend with them to produce a non-directional efiect.

A plurality. of piezo-electric drivers M are connected by arms Fig. 10 shows a modified form of connection between the composite diaphragm and a single piece electric driver. The diaphragm in this case may be of the same form as that shown in Fig. 1 except that in. place of the ring a spider 55 is employed. The piezo-electric driver is then connected by a driving rod 51] to the center of the spider.

Fig. ii shows a slightly modified construction in which a spider dd is employed instead of spider 5b and four drivers ti are connected by rods 62 to the rim of the spider.

In all of the constructions so far described a common drive is provided for the inner and the outer portions of the diaphragm. In Fig. 12 I show a construction whereby the two parts of the diaphragm may be separately driven. In this construction the outer portion of the diephragm consists of a truncated cone which is provided with a bead bit at its smaller end, this bead being engaged by a light ring at. i The in, ner portion of the diaphragm is in the form of a cone dd provided at its base with w outwardly,

extending flange 69. This cone and its flange are made of stifi material. An annular ring ll! of flexible material connects the flange 69 to the ring 61. Two sets of piezo-electrical drivers are used. An outer set of drivers H is connected by rods 12 to the ring 61 so as to directly drive the outer portion 65 of the diaphragm. An inner set of piezo-electric drivers 13 is connected by rods 14 to the flange 69 of the cone 68. By this means each portion of the diaphragm may be individually and separately driven so that one portion will not exert a mechanical damping effect upon the other. It will be understood, of course, that the ring is an air-tight connection between the two diaphragm sections. With this arrangement the voltage impressed upon the inner drivers 13 should be less than that imposed upon the outer driver H so that the former drivers will not be bent beyond their rupture point. Either the same or difierent frequencies may be fed to each diaphragm section as desired by using different input impedances, filters, different sources of voice frequency, etc.

I have shown a number of forms of my invention to illustrate the widerange of usefulness and adaptation of the invention. It will be understood, however, that these are not to be taken as limitative, but merely as illustrative and that I reserve the right to make such changes in form, construction, and arrangement of parts, as may fall within the spirit and scope of the following claims.

I claim:

1. In a loud speaker, a composite diaphragm comprising a smooth flexible outer concave portion and a relatively stiff inner convex portion peripherally joined to the outer portion,-the inner portion being of smaller area than the outer portion, and driving means connected to the relatively stiif portion.

2. In a loud speaker, a-composite diaphragm comprising a pair of reversely disposed conical portions with the larger end of one portion joined to the smaller end of the other portion, one of said portions being relatively stiff and the other being smooth and freely flexible, and driving means for the diaphragm connected to the relatively stiff portion.

3. In a loud speaker, a composite diaphragm comprising a relatively stiff central portion in the form of a cone with its apex outwardly disposed and a smooth and freely flexible outer portion in the form of a frusto-conical wall reversely disposed with respect to the cone, the smaller end of the outer portion being joined to the base of said cone, and a plurality of driving means for the diaphragm connected thereto respectively at spaced points along the junction of said portions.

tion, and a plurality of driving means for the diaphragm connected thereto respectively at spaced points' along the junction of said portions.

5. In a loud speaker, a,composite diaphragm comprising a central convex portion and an outer concave portion, the latter consisting of a relatively flexible wall and the inner portion being relatively stiff, a flexible connection between the two portions, and separate driving means for the inner and outer portions.

6. In a loud speaker, a composite diaphragm comprising a central convex portion and an outer concave portion, the latter consisting of a relatively flexible wall and the inner portion being relatively stiff, a flexible connection between the two portions, piezo-electric driving means for the inner portion of the diaphragm, and separate piezo-electric driving means for the outer portion of the diaphragm.

7. In a loud speaker, a composite diaphragm comprising a central convex portion of relatively stiff material and an outer concave portion forming a smooth frusto-oonical surface, the smaller end of the outer portion being joined to the periphery of the central convex portion, said outer portion being formed of a sheet of cloth with the pores thereof filled to render them substantially impervious without destroying the flexibility of the cloth, the depth of the outer portion as measured along its axis being greater than that of the central portion.

8. In a loud speaker, a composite diaphragm comprising a central convex portion consisting of a cone of relatively stiff material and an outer concave portion, in the form of a frusto-conical wall, the smaller end of the outer portion being joined to the periphery of the central cone and the faces of the two portions forming an angle of about 90 degrees to each other, said outer portion being formed of a sheet of cloth with the pores thereof filled to render them substantially impervious without destroying the flexibility of ,the cloth, said cloth providing a smooth frusto-conical surface, the depth of the outer portion as measured along its axis being greater than that of the central portion, and a plurality of driving means for the diaphragm connected thereto respectively at spaced points along the junction of said portions.

ROMEYN B. SCRIBNER. 

